Interannual mode of sea level in the South China Sea and the roles of El Nino and El Nino Modoki

ENSO-scale variation of the summer ocean circulation in the South China Sea (SCS) is investigated. The interannual mode of SSH features a north-south dipole pattern that modulates the cold jet off Vietnam. During the summers before and after the El Nino, the mode has opposite signs of extrema. Strengthened circulations couple with the cold SSTAs during the El Nino developing summers; weakened circulations accompany the warm SSTAs during the decaying summers. Heat advection by the basin circulation modulates the SST variation. The impact of the 1997 El Nino on the SCS circulation contrasting that of 1994 and 2002 El Nino Modoki is assessed. With moderate SST warming but further westward shift of the low-level convergence of the atmosphere in the equatorial Pacific, the El Nino Modoki phenomenon enhanced the western North Pacific summer monsoon inside the SCS, driving stronger circulations in both the summers of 1994 and 2002.